In recent years, one method of producing hydrocarbons from subsea wells has involved the use of a turret moored hydrocarbon production vessel. The turret is typically placed within or adjacent to a surface vessel which receives hydrocarbons through production risers connected to wells on the sea floor. Mooring lines are used to hold the hydrocarbon production vessel in place.
The turret allows the hydrocarbon production vessel to weather vane in response to environmental forces, while continuing to receive hydrocarbon fluids from subsea wells.
In very deep water, it is impractical to connect production risers from the wells on the sea floor directly to the turret of the hydrocarbon production vessel due to the weight of the production risers. Additionally, in harsh environments, the hydrocarbon production vessel located at the sea surface may experience large horizontal and vertical motions due to the environmental forces of wind and waves. These large horizontal and vertical motions of the turret of the hydrocarbon production vessel can result in large unacceptable bending, tension and compression fluctuations and excessive fatigue loadings in the production risers. Such bending, tension and compression fluctuations may eventually damage the production risers or in the worst case render the production risers completely unusable.
There is, therefore, a need in the art to both provide a system which can both be used in deep water with hydrocarbon production vessels and which will also decouple the effects of the large horizontal and vertical motions of the turret of such a hydrocarbon production vessel from the production riser system. Such system should not interfere with the mooring lines connected to the turret of such a hydrocarbon production vessel to hold the vessel in place.